1. Field of Invention
The disclosed invention generally relates to the field of cellular wireless communications networks. In particular, it relates to mini base stations also known as small cells, where an interface is defined between base stations to dynamically exchange neighbor topology information, which helps reduce inter-cell interference in real-time, especially for areas of large small cell deployments.
2. Discussion of Related Art
It is possible to improve network coverage and performance by overlaying low-power and low-cost small cells over existing cellular networks composed of macrocells to turn them into “heterogeneous” networks. Likewise, the 3rd Generation Partnership Program (3GPP) defined an architecture for Long Term Evolution (LTE) networks where macro base stations (so-called ‘evolved Node B’, ‘eNB’ or ‘macrocell’) and small base stations (so-called ‘Home eNB’, ‘HeNB’ or ‘small cell’) may simultaneously be deployed to improve data carrying capacity and network throughput. In the specification, eNB refers to a macro base station whereas HeNB refers to a small cell base station.
Small cells include consumer-deployed mini base stations that use the Internet as backhaul (DSL, cable etc.) to provide cellular services to consumer's premises. Small cells may also be deployed within commercial areas such as malls and enterprise offices. Obviously, it is required that small cells avoid interference with the macrocells and neighboring small cells through a careful power control, frequency and time allocation. Therefore, small cells in close proximity to each other need to somehow coordinate the use of all network resources.
Although 3GPP provides standards for base stations to form direct links to the Operations & Maintenance (OAM) components of the network for configuration and to interface with one another (i.e., X2 interface) to share certain set of information, dynamic management of interference between base stations still remains unaccounted for. When a small cell is auto-configured, it needs to discover the radio environment and learn about the properties of nearby base stations, which is used by the small cell base station to control the frequency, time and transmission power in use. Thus, the LTE small cell base station needs to detect its neighbors, and if the frequency band and time slot it intends to use is already occupied by another nearby small cell base station, it must either avoid that band or negotiate with the neighbor base station a partitioning of the band and/or other resources dynamically. Furthermore, if it is the ‘critical’ base station as defined in this invention, it may have to decrease its power usage. In order to perform these steps, a neighbor topology discovery procedure is executed between neighbor base stations forming the main part of the invention. Note that the frequency domain, time domain and power domain resource partitioning are combined.
There are several prior art related to interference management. For example, in the published U.S. Patent Application 20110249642 entitled, “Adaptive Resource Negotiation between Base Stations for Enhanced Interference Coordination” by Song et al., methods and apparatus for supporting adaptive resource negotiation between eNBs for enhanced inter-cell interference coordination (eICIC) are provided. What is disclosed is a resource status message sent by a first base station to a second base station and a proposed resource partitioning status message prepared by the second base station which takes into account the resource status message received from the first base station and optionally a number of parameters related to resource usage. The basic idea is to eliminate interference by making the base stations yield some of the resources that are concurrently being used for the sake of the other base station. In a radio access system using orthogonal frequency division multiplexing (OFDM) such as LTE systems, the yielded resources may be time based, frequency based, or a combination. Thus, this application proposes a method to realize sharing of bands between closely-located (dangerous) small cells, where the interfering base station yields subcarriers in the frequency domain. This is accomplished in a distributed manner through message exchanges between two base stations to make a decision regarding partitioning of resources between the two, without resorting to a central management entity. However, this patent application does not discuss the topology discovery between small cells.
In the published U.S. Patent Application 20090081955 entitled, “Method for Reducing Interference in a Cellular Radio Communication Network, Corresponding Interference Coordinator and Base Station” by Necker, there is a central interference coordinator which receives interference parameters in the form of measurement reports from base stations at predefined time intervals. The central coordinator determines resource allocation and not the base stations themselves. Unlike the current invention, this algorithm does not work in real time, since the central coordinator awaits interference parameters from base stations and there is a delay associated with the reporting of these parameters which takes place at preset times.
To complement techniques that assign sub-bands (group of subcarriers) to different base stations with those which perform power adjustment, in the International Patent Application No. PCT/GB2012/052511 methods of controlling the power allocated to different sub-bands by individual base stations are introduced. These methods aim to increase power in a particular sub-band only if it is advantageous to do so, where one or more users will enjoy higher bit rates or higher qualities of service. For implementing such a method, base stations need to exchange information regarding the sensitivities of the users they serve to powers allocated in that sub-band by other base stations.
The prior art, however, fails to teach an interface between base stations that allows for topological discovery to enable coordinated resource usage.